SU: Could an unclean shutdown cause a file with outstanding writes to become sparse after fsck?

[Ryan Stone]

Today I encountered a system running a very old version of FreeBSD
(6.1-ish) that was stuck in a reboot loop.  I was eventually able to
discover that the system was running into a long-since fixed bug where
the system would panic if you tried to execute a sparse file.  From
what I've been able to get from the owner of this system, it sounds
like the machine reset during a system upgrade.  I suspect that the
initial reset was unrelated (a different long-since fixed panic or a
power loss, maybe), and that some executables that had outstanding
writes before the reset ended up becoming sparse when fsck was run.
Is this possible?  The filesystem was running soft-updates, and I'm
really not familiar enough with either soft-updates or even the UFS
on-disk metadata to say whether this is reasonable.